TPMODE

TPMODE is an obsolete parameter since tape is no longer used.

TPMODE sets the number of passes at each head index
position. Allowed values are 1, 2, 4, and 8. For these cases, a
maximum of 32, 16, 8, or 4 heads can be used at a time. TPMODE=1
is appropriate for Mark III mode A, while TPMODE=2 is used for
Mark III mode B. Setups with different values of TPMODE
may be specified for a station during an experiment, but SCHED
will determine the lowest value specified for the station for the
whole experiment and use that for all scans. Thus during the times
when the setup calls for fewer heads than could be used with the
minimum TPMODE, some tracks will be left blank. This wastes
tape, but saves a great deal of complexity in keeping track of
where data should be recorded on the tape. It is strongly advised
that all setup files for a project use the same TPMODE.
Note, however, that different stations can use different TPMODES without wasting tape.

The correct TPMODE can be determined from the FORMAT, the number of bits per sample (BITS), and the number of channels (NCHAN.
Those parameters tell how many tracks are needed per channel and,
multiplied by the number of channels, how many tracks are needed per
pass. For VLBA formats, that total number of tracks is divided into
32 to get TPMODE. For Mark III, observations, the total number
of heads available is normally 28, although the VLBA systems can
record 32 tracks in Mark III format.

SCHED will derive a reasonable default for TPMODE in almost
all cases so it is not necessary to specify it.

TPMODE can be used to force a format if FORMAT is not being
specified, as is reasonable in station independent setup files. A fan
out will be chosen that generates the requested number of passes per
head position. If the observation uses wide band, 2 head (Mark IV and
VLBA4) or 2 tape (VLBA) mode, the fan out will be chosen assuming that
all antennas have the 2 head/tape capability. Later, for single drive
stations, the number of channels will be cut in half.

For S2 recorders TPMODE denotes the number of groups the S2
recorder can use in the desired recording mode. In other words it is
the total number of recorders divided by the number of recorders
implied by the mode. It must be consistent with the S2 mode implied by
the number of channels and bandwidth to be record.